1. Technical Field
This invention relates to rotary, sleeve and disc valves made of carbon fiber reinforced carbon composite materials, for use in internal combustion engines and the like.
2. Description of the Related Art
Current internal combustion, 4-cycle engines use metal poppet valves. While 2-cycle engines still use reed, disc, and rotary valves, stricter air pollution standards are causing manufacturers to turn to poppet valves even for these engines. Most poppet valves are cast, forged, or machined from billets of metal. These valves are inherently heavy and have poor structural properties at higher temperatures. By design, poppet valves must reciprocate: starting from a full stop and accelerating to very high speeds, only to be brought to a stop again and reaccelerated and brought again to a stop at the place it started. Due to their significant mass, metallic valves develop substantial inertia as engine speed (revolutions per minute or "RPM") increases. Almost all production poppet valves are restrained by metallic springs. However, as RPM increases, the spring's ability accurately to restrain the poppet valve's travel is overwhelmed by the valve's inertia and it "floats". This tendency to float inhibits the engine's ability to reach higher RPM, where more power can be produced more efficiently.
Over the years, many poppet valves have been designed to control valve motion, even at high RPM. Ducati Mechanic, Spa., the Italian manufacturer of road and racing motorcycles, uses a fully mechanical poppet valve opening and closing, "desmodromic" system. The efficacy of this design has never been conclusively established and it is an extremely expensive system to manufacture and maintain. Electrically operated poppet valves are currently being tested, but they have not yet been shown successfully to operate at even moderately high RPMs. International Formula 1 racing teams have in recent years employed pneumatic springs to overcome the limitations of metal springs. It is not clear when or if these designs will be put into production engines, but it will be recognized that these systems do not avoid the basic problem: poppet valves must reciprocate.
In production engines, the tendency of poppet valves to float is compensated for by the use of increasingly stiff springs. However, increasing spring stiffness also increases the work the engine must perform just to open the valves, and this in turn results in significant power drain. Moreover, poppet valve systems are major contributors to the overall noise produced by an engine. Stiffer springs tend to result in noisier valve trains. More efficient and powerful and quiet engines could be designed if a satisfactory alternative to the poppet valve could be found.
Another inherent problem with poppet valves is the fact that they stand directly in the path of the intake and exhaust charges they are meant to admit and discharge. Over the years almost every variation in combustion chamber shape, valve position, and manifold design has been tried to maximize the amount of charged fuel that can flow past a poppet valve into the chamber. The current trend has been to give the intake charge (and, to a lesser extent, the exhaust charge as well) as straight a path as possible into the combustion chamber. Nevertheless, the poppet valve still stands in the way. The ability of an engine to admit a charge efficiently could be significantly improved if an unblocked path into the combustion chamber could be designed.
Another inherent problem with metallic poppet valves is that they quickly lose strength as temperatures increase. Low cost, commodity steel poppet valves used in the overwhelming majority of combustion engines are limited to exhaust gas temperatures in the 1500 to 1750 degree Fahrenheit range. Combustion efficiencies could be improved and undesirable emissions reduced if exhaust gas temperatures could be raised beyond this level.
Over the years engineers have proposed the use of rotary, sleeve, and disc valves to overcome the inherent limitations of the poppet valve. The basic design of these valves is to rotate a valve body to expose and close intake and exhaust ports. In this way, the need to reciprocate a poppet valve is avoided. There are three very general designs of rotary valves: cylindrical, sleeve, and disc. One type of cylindrical rotary valve is open at each end and separated inside by a wall, creating two chambers, each ported to the combustion chamber through windows in the side of the cylinder. Another type of cylindrical rotary valve is substantially solid and has in its sides one or more recesses that expose the combustion chamber to a manifold. These two types of cylindrical rotary valves have axes of rotation that are perpendicular to the cylinder. Another type of rotary valve has its axis of rotation parallel to the cylinder. One such type is in the general shape of a cone, the base of which is exposed to the combustion chamber. A port from the base and through the side of the cone permits gases to be admitted or expelled. The sleeve valve is in the shape of a cylinder and also acts as the cylinder in which the piston reciprocates. The sleeve valve rotates, and in some cases also reciprocates, exposing ports. The disc valve can operate in substantially the same manner as the cone-shaped rotary valve, or it can operate at different positions, such as at the side of the cylinder, as is the general practice with 2-cycle disc valves. Rotary valves in 4-cycle engines have never seen volume production. Sleeve valves have been used in production aero engines, but have never gained wide favor.
The principal of these valve designs is that the rotary valve and the surface it rides in must be very closely mated in order adequately to seal the combustion chamber, but as engine temperatures rise the different expansion rates of these metallic parts leads either to sealing problems, if the parts are not close enough, or to seizure, if they are too close. An additional defect of these designs is that they are difficult to lubricate and when they are adequately lubricated they tend to admit lubricating oil into the combustion chamber, leading to undesirable emissions. Moreover, if a metallic rotary valve is used to discharge exhaust gases it will tend to become extremely hot and difficult to lubricate.
The present invention overcomes the traditional problems associated with rotary, sleeve, and disc valves by constructing them of a carbon fiber reinforced carbon composite ("CFRCC") material, as more fully described below.